Do you mean playback quality specifically or overall image quality?
Overall video quality in playback (recording quality) John.
You could record video uncompressed :)
The question's still really too broad but here are a few general drivers impacting recording quality:
- What's the compression level? Sometimes vendors set it too low to save on bandwidth but reduce image quality (see DVTel). Alternatively, even with responsible manufacturers, you might want to decrease the compression level a little to get a quality boost (but typically it won't be much and it can come at a steep bandwidth cost).
- Are you using CBR and is the rate too low? While I think CBR should be avoided, if you have to use it, make sure it is high enough to cover the most demanding times of day. Otherwise, recording quality will decrease. See our streaming recommendations (CBR, VBR, VBR with Cap).
Focusing: If you really want to ensure quality video over time, I think using cameras with built in auto focus / ABF is critical.
One important element that also needs to be considered is what the VMS is configuring vs what is configured in the camera. Sometimes, the VMS will make its own decisions about low level stream settings without clearly acknowledging/showing what they are. This can create problems even if you have 'properly' set up the camera in its own web interface.